1. Field of the Invention
This invention relates to the field of video signal encoding, and in particular to a method and means for inserting code signals at certain line positions within the vertical interval of a video program signal.
2. Description of the Prior Art
Inserting code signals or words at designated line positions within the vertical interval of a standard video program signal is well known in the art. For example, U.S. Pat. No. 4,332,022, issued May 25, 1982 and assigned to the assignee of the present invention and entitled TRACKING SYSTEM AND METHOD FOR VIDEODISC PLAYER, shows and describes the manner in which stop motion is accomplished in a videodisc player by the recognition of a white flag occurring during the vertical interval of the program recorded on the videodisc. In such a system, upon detecting the presence of a white flag in the vertical interval, and having enabled the stop motion circuitry for performing retracing motions of the last-read information track, the optics of the videodisc player are driven to cause the read beam to retrace the last-read track. Upon again detecting the white flag, the player effects another retrace, and this process continues until another instruction is received by the player to cease the stop motion function.
Similarly, in a copending U.S. application No. 161,231 filed June 19, 1980, a divisional application of Ser. No. 066,620 now abandoned, filed Aug. 15, 1979 and assigned to the assignee of the present invention, entitled "VIDEO RECORDING MEDIUM FOR STOP-MOTION PLAYBACK", a stop-motion data flag is inserted during the vertical interval to indicate which frame contains compressed audio information.
In both of the aforementioned systems, insertion of the white flag or data flag signals is accomplished by routing the program signal through a summing amplifier, a second input to the summing amplifier being the white flag signal occurring in its proper time relationship to the program signal. The output of the summing amplifier is then the sum of the two signals, i.e., the program signal with the data flag inserted at the proper location in the vertical interval. If the data flag is to be inserted only on certain fields, for example only on odd fields or only on even fields, an operator must set the data flag generator to produce a flag at alternate field positions and manually synchronize the program signal with the data flag signal until the data flag is placed in the proper, or desired, even or odd numbered fields.
One problem associated with the prior art attempts at synchronizing a data flag signal with program material arises from the inability to begin or end placement of the vertical interval code at precise locations in the program material. That is, it is a relatively simple matter to combine a program signal and a vertical interval code signal in a summing amplifier for continuous summation of the two signals. However, it is often desirable in formatting videodiscs to identify, with frame accuracy, a lead-in portion by a particular code in the vertical interval, to identify active program material at a precise start point and end point, and to identify the beginning of a lead-out portion on the disc. Using the manual techniques described above, this was simply not possible. Furthermore, without the ability to precisely locate the vertical interval codes, proper placement was often found only by a trial and error method by which an operator would observe the location of the code signal in the vertical interval after the program material is started up, and if the code occurred at the wrong location, e.g., in an even field when it should have been in an odd field, a restart of the summing process was necessary.
A technique which offered improvement over the prior discussed manual method of inserting vertical interval codes in existing video program material, utilized the location and tracking principles involved in video editing. In such an arrangement, a video tape was prepared containing the program material, and a second video tape was prepared containing only the vertical code signals arranged in association with a composite sync signal produced by an appropriate signal generator. An operator would then load both tapes into corresponding tape players, and by operating the slow search controls of a video editing controller would locate the proper field (at the desired frame number) on the tape containing only sync and code information, would locate the proper field (at the desired frame number) on the program material tape, and perform an edit function. The two signals on the two tapes would then proceed in synchronization with one another for the length of the program, and a summing amplifier could then be used to sum the two signals together in a manner similar to that described with the manual operating procedure discussed earlier. By using the editing controller, at least the trial and error method was avoided, since the proper program field for insertion of the vertical interval code was chosen by the editing operator. Furthermore, the editing procedure assures that the vertical code signals will begin precisely and end precisely at desired points in the program. It can be appreciated, however, that such a procedure is extremely time consuming both in delay of processing and in accumulated operator labor hours. Additionally, this procedure ties up an expensive editing system for considerable time.
Accordingly, there is a need in the art for a system which can insert vertical interval code information into the appropriate vertical interval of a video program utilizing more automatic encoding techniques and avoiding the time comsuming and expensive editing procedures used in the past. The present invention provides such a system.